Many people experience adverse conditions associated with functions of the cortex, the thalamus, and other brain structures. Such conditions have been treated effectively by delivering electrical energy to one or more target areas of the brain. One method of delivering electrical energy to the brain involves inserting an electrical stimulation lead through a burr hole formed in the skull and then positioning the lead in a precise location proximate a target area of the brain to be stimulated such that stimulation of the target area causes a desired clinical effect. For example, one desired clinical effect may be cessation of tremor from a movement disorder such as Parkinson's Disease. A variety of other clinical conditions may also be treated with deep brain stimulation, such as essential tremor, tremor from multiple sclerosis or brain injury, or dystonia or other movement disorders. The electrical stimulation lead implanted in the brain is connected to an electrical signal generator implanted at a separate site in the body, such as in the upper chest.
Chronic pain afflicts approximately 86 million Americans and it is estimated that United States business and industry loses about $90 billion dollars annually to sick time, reduced productivity, and direct medical and other benefit costs due to chronic pain among employees. Because of the staggering number of people affected by chronic pain, a number of therapies have been developed that attempt to alleviate the symptoms of this condition. Such therapies include narcotics, non-narcotics, analgesics, antidepressants, anticonvulsants, physical therapy, biofeedback, transcutaneous electrical nerve stimulation (TENS), as well as less conventional or alternative therapies. Other treatment options involve neuroaugmentive techniques such as spinal cord stimulation or intrathecal pumps. For a subset of patients, however, these therapies are inefficacious and more invasive procedures such as blocks, neurolysis and ablative procedures become the only options for treatment. In particular, ablative procedures, although infrequently utilized, are the primary alternative for patients unresponsive to other modes of treatment. Such procedures, however, have the fundamental limitation of being inherently irreversible and being essentially a “one-shot” procedure with little chance of alleviating or preventing potential side effects. In addition, there is a limited possibility to provide continuous benefits as the pathophysiology underlying the chronic pain progresses and the patient's symptoms evolve. Because of the inherent disadvantages of ablative procedures, electrical stimulation of the brain has become an attractive neurosurgical alternative to alleviate the symptoms of chronic pain.
Electrical stimulation of the brain for chronic pain has been used since the 1950s when temporary electrodes were implanted in the septal region for psychosurgery in patients with schizophrenia and metastatic carcinoma. In particular, electrodes were placed in the septum pellucidum in a region anterior and inferior to the foramen of Monro. In the in six patients with intractable pain, but successful pain relief was obtained in only one patient. Despite these earlier reports of septal and caudate stimulation, current applications of electrical stimulation for pain involve thalamic, medial lemniscus, internal capsule stimulation, periventricular gray and pariaqueductal gray stimulation. For example, thalamic stimulation for pain relief was first reported for stimulation along the ventroposterolateral nucleus and ventralis posterior to relieve chronic intractable deafferentation pain and stimulation along the ventroposteromedial nucleus to relieve refractory facial pain. With respect to internal capsule stimulation, chronic stimulating electrodes have been implanted in the posterior limb of the internal capsule in a number of patients, including patients with lower-extremity pain and spasticity following spinal cord injury.
Although the above-mentioned target sites are all deep brain stimulation target sites, several studies have supported the role of motor cortex stimulation for pain control. For example, in the process of performing sensory cortex stimulation in an attempt to relieve thalamic pain, it was found that stimulation of the precentral gyrus/motor cortex was effective in relieving thalamic pain. Interestingly, stimulation of the sensory cortex exacerbated the pain in many patients.
Therefore, despite previous attempts to alleviate the symptoms of chronic pain by deep brain or cortical stimulation, there is still an unmet need for a method of treating chronic pain that is effective in a larger subset of the patient population.